1. Field of the Invention
The present invention relates to an ink jet recording head and an image recording apparatus which can obtain output images satisfying needs of industries in a wide range of field including a printing industry where a high-speed outputting of high-quality images is required, a printer industry which must meet office and personal demands and a consumer article industry which requires low-cost general-use output equipment capable of using versatile recording sheets.
2. Description of the Related Art
A constitution of a conventional electrostatic acceleration type ink jet recording head is explained hereinafter in conjunction with FIG. 15. The recording head is constituted such that ink 111 is filled in a slit defined by slit members 112, 113. A plurality of electrodes 114 which apply a voltage to ink are disposed in the inside of the slit member 112. Ink 111 is fed to a distal end of the head by way of an ink supply passage not shown in the drawing.
By applying a voltage to every other electrode 114 from a power supply not shown in the drawing and grounding other electrodes, electric fields are generated around electrodes to which the voltage is applied. At this point of time, with respect to ink 111 filled in the inside the slit, raises 1R of a liquid surface are formed at the electrode portions to which the voltage is applied. Although an applied signal necessary for ejecting ink must be not less than 3 msec, when the voltage of xe2x88x92200 V is applied to the electrodes 114 of the slit member 113, the raises of approximately 50 xcexcm are formed at the voltage-applied electrode portions. By arranging a counter electrode not shown in the drawing at a position where the counter electrode faces the above-mentioned raises of the ink liquid surface in an opposed manner and then applying a signal voltage of 500 V and 300 xcexcsec having rectangular waves to these electrodes, ink droplets are ejected from the raised portions of the ink liquid surface corresponding to the magnitude of applied signal and circular pixels having a diameter of approximately xcfx86150 xcexcm are formed on a recording sheet (see Japanese Patent. No. 1987697).
The recording head and the recording method used in the conventional electrostatic acceleration type ink jet recording system have following drawbacks.
That is, by preliminarily forming raises of ink by applying a voltage to ink, following problems arise.
(1) A separate drive circuit becomes necessary besides driving for ejecting ink.
(2) To ensure forming of raises of ink having a stable shape, it becomes necessary to generate the stable electric field and hence, there may be a case that additional electrodes are necessary besides electrodes for ejecting ink.
(3) Since it is necessary to preliminarily apply a voltage to ink, ink may be charged at positions other than desired pixel positions and hence, there may be a case that dot printing cannot be obtained at desired positions.
(4) Since shape of the raises of ink such as the width thereof in a lateral direction of an opening portion or the radius of curvature thereof are adjusted electrically, the shape is liable to be influenced by moisture, temperature and physical properties of ink and hence, it is difficult to form the shape of ink raises in a stable manner. Further, since the diameter of dots to be printed is largely influenced by the magnitude of the shape of the raises of ink, it has been difficult to control the diameter of dots to be printed to a fixed size.
(5) With respect to the ink jet recording head having a slit-like opening portion, at the time of performing a continuous printing, the supply of ink cannot follow the printing in the vicinity of the center of the opening portion and hence, the shortage of ink supply occurs there. Further, in the longitudinal direction of the slit opening portion, since a charge generated by the electric field concentration is liable to be stored in ink at head end portions, a larger amount of ink is liable to be ejected from the end portions. Accordingly, in the longitudinal direction of the opening portion, the diameter of dots to be printed becomes larger at the end portions than at the center position.
In an ink jet recording head and an image recording apparatus according to the present invention, the profiling such as chamfering or forming of steps is performed on a support body that defines a slit-like opening. To be more specific, an ink raise portion formed in a periphery of the opening portion on the support body is processed such that a width in the lateral direction (hereinafter called xe2x80x9cink raise widthxe2x80x9d) of a bottom surface portion with which ink comes into contact (hereinafter called xe2x80x9cink holding bottom surfacexe2x80x9d) is set to a desired width thus forming ink raise width setting means.
Alternatively, surfaces other than the ink holding bottom surface in the vicinity of the opening portion are made of an oleophobic or hydrophobic component and further the ink holding bottom surface is made of an oleophilic or hydrophilic component. Due to such constitutions, the ink raise width in the lateral direction of the opening portion can be easily controlled to a fixed value without using a method such as an electric drive so that the diameter of dots to be printed can be controlled in a stable manner.
Further, by setting the value of the ink raise width to a value of a given rate relative to the size of dots to be printed, a desired size of dots can be set and the printing can be performed in a stable manner.
Still further, by providing the above-mentioned ink raise width setting means to respective positions of recording electrodes disposed at the above-mentioned opening portion, the number of defective dots can be reduced.
In addition, by increasing the value of the ink raise width in the support body in the vicinity of a central portion of the opening portion than end portions of the opening portion in the longitudinal direction of the opening portion, the diameter of dots to be printed is prevented from becoming irregular in the longitudinal direction of the opening portion.